The present invention relates to a film which can be formed into a pouch with an easy open feature. This thermoplastic film can be used to make vertical form/fill/seal (VFFS) packages for a wide variety of food and non-food items.
Vertical form/fill/seal (VFFS) packaging systems have proven to be very useful in packaging a wide variety of flowable products. An example of such systems is the ONPACK(trademark) flowable food packaging system sold by W. R. Grace and Co.-Conn. through its Grace Packaging group. The VFFS process is known to those of skill in the art, and described for example in U.S. Pat. No. 4,589,247 (Tsuruta et al), incorporated herein by reference. A flowable product is introduced through a central, vertical fill tube to a formed tubular film having been sealed transversely at its lower end, and longitudinally. The pouch is then completed by sealing the upper end of the tubular segment, and severing the pouch from the tubular film above it.
The choice of packaging materials is important, and should be matched to the intended end use of the pouch.
Several ways of dispensing the contents of such pouches at their point of use, such as a restaurant, commissary, or the like, have been proposed. One is the use of an internal fitment sealed to the interior surface of a pouch wall, such as the ASEPT(trademark) fitment distributed in the U.S. by the assignee of the present application, and disclosed in U.S. Pat. No. 4,603,793 (Stern). In use, a coupling device would be inserted through the pouch material to communicate with the internal fitment, and a conventional dispensing device would be connected to the coupling device for delivering measured portions of the contents of the pouch.
An alternative technique and apparatus for dispensing the contents of a pouch is the use of a pouring spout such as the TOP-TAP(trademark) pouring spout supplied by DuPont Canada, and described in differing embodiments in their Canadian Pat. No. 1,192,164 (Obidniak) and U.S. Pat. No. 5,325,995 (Harrison et al). This system involves piercing the filled pouch with the sharp end (piercing nozzle) of a pouring spout, and driving the piercing nozzle into the pouch interior until the laminate forming the pouch wall engages the shoulder of the piercing nozzle. When this occurs, the plastic material forming the pouch will dispose around the shoulder of the nozzle, to be secured by a collar. The pouring spout can then be used to dispense the contents of the pouch.
In some cases, a packager may wish to forgo the use of internal or external fitments because of the additional packaging cost associated with such devices.
An alternative is simply to cut open the pouch with a knife at the time that it is desired to access the contents of the pouch, e.g. at the time that the contents of the pouch are to be placed in a dispenser. However, this procedure, although simple, exposes the user to the possibility of injury when cutting open the pouch. Even if the cutting/opening operation is done without injury, this procedure leaves the choice of where to cut the pouch to the person opening the pouch, which can cause spillage of the contained product. Additionally, for insurance reasons, many restaurants, such as some fast food outlets, do not permit knives or the like in the food preparation area of the restaurant.
It would thus often be desirable to avoid the necessity of using fitments, and the haphazard use of a knife or other sharp object to open the pouch, and to provide that the pouch could be simply and easily torn open at a preselected point on the pouch, chosen to make the opening process easier and reduce potential spillage.
However, many VFFS and other packaging applications require the use of packaging materials, especially flexible packaging materials, that can be used to package food or non-food articles and protect these articles during storage and distribution. Where flowable foods are packaged, as in many VFFS applications, the hydrostatic pressure of many oil and water based foods requires a tough, impact and abuse resistant packaging material that will maintain its structural integrity during the packaging process, and subsequent distribution and storage. Film technology has progressed to the point where many films offer a high degree of abuse resistance. Unfortunately, the same properties of toughness and abuse resistance that are desirable for the performance of the packaging material in protecting the contained article, often make it difficult or impossible for the end user to manually open the package without the aid of a knife or the like.
Various solutions to this problem have been proposed with a view to overcoming this problem and making it easier to open packages of the type just described. One is the use of tear notches, perforations, slits, etc. which guide the user to a particular place on the pouch to initiate tear.
However, providing for tear initiation and placement is often not enough. The packaging material must have low enough tear propagation so that the material will continue to tear easily beyond the end point of a tear notch or the like. If tear propagation values for the material are too high, the material will stretch rather than tear, and make it very difficult to properly tear open the pouch.
It would therefore be of great benefit to the packaging industry to provide an easy open tear film compatible with current commercial packaging systems, i.e. a film having good dimensional stability and abuse resistance.
In one aspect of the invention, a film coextruded comprises a core layer comprising a polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each disposed on a surface of the respective intermediate layer, comprising an ethylene/alpha olefin co-polymer; wherein the two outer layers each comprise at least 27% of the total thickness of the film.
In a second aspect of the invention, a process for making a film comprises coextruding a film comprising a core layer comprising a polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each disposed on a surface of the respective intermediate layer, comprising an ethylene/alpha olefin copolymer; and blowing the film by a hot blown process up to a blow-up ratio of between 2.0:1 and 3.0:1.
In a third aspect of the invention, a package comprises a flowable food product; and a pouch containing the food product, the pouch made from a film comprising a core layer comprising a polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each disposed on a surface of the respective intermediate layer, comprising an ethylene/alpha olefin copolymer; wherein the two outer layers each comprise at least 27% of the total thickness of the film.
The term xe2x80x9ccore layerxe2x80x9d as used herein refers to the central layer of a multi-layer film. In the present invention, it can comprise either a single polyamide layer, or three layers wherein two layers of polyamide have therebetween a layer comprising an adhesive.
The term xe2x80x9couter layerxe2x80x9d as used herein refers to what is typically an outermost, usually surface layer of a multi-layer film, although additional layers and/or films can be adhered to it.
The term xe2x80x9cintermediatexe2x80x9d as used herein refers to a layer of a multi-layer film which is between an outer layer and core layer of the film.
xe2x80x9cPolymerxe2x80x9d herein includes homopolymer, copolymer, terpolymer, etc. xe2x80x9cCopolymerxe2x80x9d herein includes copolymer, terpolymer, etc.
xe2x80x9cPolyamidexe2x80x9d is used herein to mean both polyamides and copolyamides, and means a polymer in which amide linkages (xe2x80x94CONHxe2x80x94) occur along the molecular chain. Examples are nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon 6/66, and amorphous nylon.
xe2x80x9cAdhesivexe2x80x9d refers to adhesives, preferably polymeric adhesives, more preferably polyolefins having an anhydride functionality grafted thereon and/or copolymerized therewith and/or blended therewith. xe2x80x9cAnhydride functionalityxe2x80x9d refers to any form of anhydride functionality, such as the anhydride of maleic acid, fumaric acid, etc., whether grafted onto a polymer, copolymerized with a polymer, or blended with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters, and metal salts derived therefrom. More generally, xe2x80x9cadhesivexe2x80x9d refers to any material that adheres a polyamide layer to another polyamide layer, or to an ethylene/alpha-olefin copolymer such as LLDPE.
As used herein, the phrase xe2x80x9cethylene/alpha-olefin copolymerxe2x80x9d (EAO) refers to such heterogeneous materials as linear medium density polyethylene (LMDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers (HEAO) such as TAFMER(trademark) ethylene/alpha olefin copolymers supplied by Mitsui Petrochemical Corporation and metallocene-catalyzed polymers such as EXACT(trademark) materials supplied by Exxon. These materials generally include copolymers of ethylene with one or more comonomers selected from C4 to C10 alpha-olefins such as butene-1. (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. Other ethylene/alpha-olefin copolymers, such as the long chain branched homogeneous ethylene/alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY(trademark) resins, are also included as another type of ethylene/alpha-olefin copolymer useful in the present invention.
xe2x80x9cLinear low density polyethylenexe2x80x9d (LLDPE) as used herein has a density in the range of from about 0.916 to 0.924 grams per cubic centimeter. xe2x80x9cLinear medium density polyethylenexe2x80x9d (LMDPE) as used herein, has a density from 0.930 grams per cubic centimeter to 0.939 grams per cubic centimeter. xe2x80x9cHigh density polyethylenexe2x80x9d (HDPE), as defined herein, has a density of 0.94 grams per cubic centimeter or more.
The term xe2x80x9cethylene/ester copolymerxe2x80x9d (E/E) as used herein refers to a copolymer formed from ethylene and an ester such as vinyl acetate, alkyl acrylate, or other monomers, wherein the ethylene derived units in the copolymer are present in major amounts and the ester derived units in the copolymer are present in minor amounts.
xe2x80x9cHeat shrinkablexe2x80x9d is defined herein as a property of a material which, when heated to an appropriate temperature above room temperature (for example 96xc2x0 C.), will have a free shrink of 5% or greater in at least one linear direction.
xe2x80x9cFlowable materialsxe2x80x9d herein means food or non-food items which are flowable under gravity, or can be pumped, as defined in U.S. Pat. No. 4,521,437 (Storms), incorporated by reference herein in its entirety.
All compositional percentages used herein are calculated on a xe2x80x9cby weightxe2x80x9d basis.